Process for operating a utility boiler and methods therefor

ABSTRACT

A process for operating a utility boiler. The process has the following steps: (a) providing fuel to the boiler; (b) providing one or more additives selected from the group consisting of (i) one or more slag control agents, (ii) one or more oxygen-generating agents, (iii) one or more acid mitigation agents, (iv) one or more fouling prevention agents, (v) one or more oxidizer agents, (vi) one or more heavy metal capturing agents, and (vii) any combination of the foregoing to the boiler or an auxiliary device thereof; (c) providing air to the boiler; (d) burning the fuel in the boiler to generate heat and an exhaust gas; (e) intermittently or continuously monitoring one or more physical and/or chemical parameters of the fuel and/or intermittently or continuously monitoring one or more emissions variables of the exhaust gas to obtain one or more values therefor; and (f) varying or maintaining the rate at which either or both of the fuel and the one or more additives are provided to the boiler based on the one or more values obtained.

CROSS-REFERENCE TO A RELATED APPLICATION

The present application is a continuation application of U.S. Ser. No.12/769,152, filed Apr. 28, 2010, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for operating a utilityboiler. The present invention also relates to a process for operating autility boiler in which physical and/or chemical parameters of the fueland emissions variables of the exhaust gas and/or flue gas of theutility boiler are monitored and fuel and/or additive feed rates arevaried accordingly.

2. Description of the Related Art

Utility boilers or furnaces are employed in industry for generation ofheat, production of steam, and generation of electricity utilizingsteam. Utility boilers typically have a furnace therein where a fuelfuel, such as coal, biomass, residual oil or #6 fuel oil, is oxidized orburned to generate heat. Along with generating heat, utility boilerswill generate or evolve an exhaust gas and/or a flue gas that willcontain carbon dioxide (product of oxidation of coal, biomass, and fueloil), residual oxygen (unreacted), inert air components, i.e., nitrogenand argon, and emissions, such as sulfur-based and nitrogen-basedcompounds. Exhaust gas and/or a flue gas is typically treated and thenvented to the atmosphere.

A variety of problems are encountered when operating utility boilers.Such problems generally relate to slag deposition, fouling, cleanliness,efficiency, and emissions.

Emissions problems relate to sulfur-based emissions, such as sulfurdioxide (SO₂), sulfur trioxide (SO₃), and sulfuric acid (H₂SO₄);nitrogen-based emissions (NO_(x)), such as emissions include nitrousoxide (NO) and nitrogen dioxide (NO₂); mercury-based emissions (Hg) andparticulates. Free sulfur trioxide in an exhaust gas and/or a flue gasimparts an undesirable opaque appearance (a blue haze or trailing plume)to the gas when vented to the atmosphere. Free sulfuric acid can causecorrosion of process surfaces in utility boilers as well as acid rain inthe atmosphere. Particulate emissions are made up of unburned carbon andash. Unburned carbon is formed when burning of oil in the boiler isincomplete. Ash is naturally present in coal and is present in fuel oilas a leftover from oil refining. Particulates also present cleanlinessand industrial hygiene problems.

Slag deposition can take the form of one or more layers caked/baked ontoprocess surfaces. The one or more layers typically contain silica,aluminum, calcium, and metal complexes of vanadium with sodium, nickel,iron, or magnesium. Slag can deposit on the surfaces of tube bundles orother heat transfer devices within the utility boiler denuding aboiler's heat transfer efficiency.

It would be desirable to have a process for operating a utility boilerwherein slag deposition, fouling, cleanliness, and undesirable emissionscan be reduced or minimized. It would also be desirable to have aprocess for operating a utility boiler that affords enhanced operationalefficiency.

SUMMARY OF THE INVENTION

According to the present invention, there is a process for operating autility boiler. The process has the steps of (a) providing fuel to theboiler; (b) providing one or more additives selected from the groupconsisting of (i) one or more slag control agents, (ii) one or moreoxygen-generating agents, (iii) one or more acid mitigation agents, (iv)one or more fouling prevention agents, (v) one or more oxidizer agents,(vi) one or more heavy metal capturing agents, and (vii) any combinationof the foregoing to the boiler or an auxiliary device thereof; (c)providing air to the boiler; (d) burning the fuel in the boiler togenerate heat and an exhaust gas and/or a flue gas; (e) intermittentlyor continuously monitoring one or more physical and/or chemicalparameters of the fuel and/or intermittently or continuously monitoringone or more emissions variables of the exhaust gas and/or a flue gas toobtain one or more values therefor; and (f) varying or maintaining therate at which the fuel and/or one or more of the additives is providedto the boiler based on the one or more values obtained.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a boiler system useful incarrying out the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the present invention, the fuel is intermittently orcontinuously monitored for one or more physical and/or chemicalparameters of the fuel to obtain one or more values therefor. The feedrates of the fuel and one or more additives to the boiler and/or anauxiliary device(s) thereof are varied or maintained based on the one ormore values obtained.

The actual monitoring on the physical and/or chemical parameters of thefuel and emissions variables of the exhaust gas and/or a flue gas cantake place intermittently or continuously as desired. In a preferredembodiment, the monitoring takes place substantially continuously, i.e.,a test is repeated as soon as it ends over a continuum of time. In otherembodiments, a period of time can elapse between the end of a test andrepeat of the test. For example, a period of time elapse can be fiveminutes or less, one minute or less, or 30 seconds or less. The valuesobtained from monitoring are used to vary the rate at which fuel and/orone or more of the additives is provided to the boiler. In a preferredembodiment, the results or values obtained in a test are used to effectvariance or maintenance of existing fuel and/or additive rates.

A preferred process of the present invention monitors the physicaland/or chemical parameters of the fuel and emissions variables of theexhaust gas and/or a flue gas in “real time”. The term “in real time”means that (a) physical and/or chemical parameters of the fuel andemissions variables of the exhaust gas and/or a flue gas are monitoredsubstantially continuously, i.e., one test is administered as soon asthe previous one is finished; (b) communication of the results or valuesobtained from the analytical testing or monitoring of physical and/orchemical parameters of the fuel and/or emissions variables to aprocessor or controller is substantially instantaneous; (c) afterresults or values are obtained, the processor or controller thensubstantially instantaneously instructs process components that effectregulation or control of feed rates of the fuel and/or the additives tovary or maintain fuel and/or additive rates, accordingly.

An embodiment of the process of the present invention has a boilersystem that includes a boiler and conduits for feedstocks, steam, andexhaust. Associated peripheral equipment, such as pumps, flowmeters, aprogrammable logic controller (PLC) interface or similar control device,and remote communication devices can be arranged on a “skid” separatefrom but in communication with the boiler along with necessary electriccabinets, wiring, plumbing, and other infrastructure. Boiler systems aretypically equipped with a host of instrumentation and diagnostic systemsrouted through a distributed control system (DCS). A DCS takes the formof control room software and a network, and interacts with one or morePLCs in the boiler's system. In a preferred embodiment, a skid has itsown PLC. Data obtained can include, for example, include fuel transferrate, coal firing rate, heat input, various boiler temperatures andpressures,

emission variables (e.g., SO₂, NO_(x), NH3, O, CO, acid level,particulates, opacity, and heavy metals such as Hg), component systemoperating parameters, and the like. Data can be transmitted to a skidand used to control and adjust process variables, such as dosage level,blend ratio, and duration of the treatment. Information is fed into aPLC and manipulated via algorithms and other programming to continuouslyadjust and optimize treatment of the fuel.

An embodiment of the process of the present invention is set forth inFIG. 1 in the form of a boiler system 10. System 10 has a boiler 12.Feed streams 14, 16, 18, 20, and 22 provide conduits for feeding a fuel,a first additive, a second additive, water, and air, respectively, intoboiler 12. Exit stream 24 delivers steam produced in boiler 12. Exitstream 26 delivers exhaust gas. Controller 28 monitors the physicaland/or chemical parameters of the fuel to obtain one or more valuescorresponding to same and provides instructions in real time to one ormore components of the process (not shown) to vary or maintain the rateat which the fuel and/or the first and second additives is provided toboiler 12.

Various additives are employed in the present invention for controllingslag formation, fouling, emissions levels, and the like.

The slag control agent can be employed in the process of the presentinvention to prevent buildup of slag deposits within the furnace of theutility boiler and other process surfaces during the combustion of thecoal, biomass, or fuel oil. The slag control agent also reacts orcomplexes with any undesirable vanadium compounds that may be present infuel oil. Conversion of undesirable vanadium compounds, such as vanadiumpentoxide and sodium vanadium pentoxide, to more innocuous vanadiumcompounds or forms helps to prevent or reduce catalysis of sulfurdioxide to sulfur trioxide, corrosion of process surfaces due to acidexposure, and deposition of vanadium compounds on process surfacesinside the utility boiler.

Useful slag control agents include, but are not limited to, thefollowing: magnesium hydroxide; magnesium oxide; magnesium carbonate;and magnesium organometallic compounds, such as magnesium carboxylate,magnesium salicylate, magnesium naphthenate, and magnesium sulfonate.Preferred slag control agents are magnesium hydroxide, magnesium oxide,and organometallic magnesium carboxylate with magnesium carbonateoverlay.

The oxygen-generating agent can be employed in the process of thepresent invention to provide additional oxygen at the situs of oxidationor burning in the furnace, which allows the feed rate of air supplied tothe utility boiler to be reduced and/or minimized. Use of theoxygen-generating agent also reduces the incidence of unburned carbondue to more efficient combustion or burning. Reduction of unburnedcarbon also reduces the incidence and retention of sulfuric acid, whichis absorbed by unburned carbon.

Useful oxygen-generating agents include, but are not limited to, thefollowing: calcium nitrate, calcium organometallic compounds, calciumsalicylate, calcium sulfonate, overbased calcium carboxylate, ironoxides, iron carboxylates, iron organometallic compounds, ironsulfonates, barium oxide, barium carbonate, barium carboxylate, bariumorganometallic compounds, and barium sulfonate. Preferredoxygen-generating agents are the calcium compounds. Most preferredoxygen-generating agents are calcium nitrate and calcium carboxylate.

The acid mitigation agents can be employed in the process of the presentinvention to reduce or minimize the amount of acidic compounds in theboiler and the exhaust gas and/or flue gas. Particularly, the agentreacts with sulfuric acid to form innocuous, non-acidic compounds,thereby reducing acid emissions in the exhaust gas and/or flue gas andcorrosion of process surfaces within the boiler. Acid mitigation agentscan either neutralize or absorb/adsorb acids. Examples of acidmitigation agents include magnesium oxide, magnesium hydroxide,magnesium carbonate, sodium bicarbonate carbonate, and calciumcarbonate.

The fouling prevention agents can be employed in the process of thepresent invention to reduce or minimize buildup on process surfaceswithin the boiler and maintain operational efficiency. Examples offouling prevention agents include magnesium oxide, magnesium hydroxide,magnesium carbonate, and

sodium borate.

The oxidizer agents can be employed in the process of the presentinvention to (i) reduce or minimize excessive makeup air addition to thefurnace and (ii) help convert mercury and heavy metal constituents to anoxidized form that is easier to capture. Examples of oxidizer agentsinclude calcium bromide,

calcium chloride, and sodium bromide.

The heavy metal capture agents and can be employed in the process of thepresent invention to reduce or minimize mercury emissions. A preferredheavy metal capture agent is a mercury capture agent. Examples ofmercury capture agents include calcium sulfide, calcium polysulfide, andsodium sulfide. Heavy metal capture agents are preferably incorporatedoutside the boiler into one of its auxiliary devices. For example, theagent can be injected into the exhaust system or added to a flue gasdesulfurization unit. The agent can take the form of a dry or wetsystem.

The additives can be added or mixed into the coal, fuel oil, or biomassprior to combustion or added into the furnace of the utility boilerduring combustion or burning. The treatment of the coal or fuel oil canbe homogeneous or non-homogeneous, i.e., the agents can be homogeneouslyadmixed within the coal or fuel oil or non-homogeneously applied, suchas to the surface or some portion of the coal or fuel oil. Someadditives may be added to a boiler system at an auxiliary devicethereof. An auxiliary device is an inlet or outlet apparatus orcomponent of a boiler outside of the furnace or direct heating sectionthereof. For instance, particularly heavy metal capture agents such asmercury capturing agents, are typically added in an exhaust systemand/or a flue gas desulfurization unit.

The additives can be used in any known product form, such as a mineralore, a powder, or liquid. Liquids may be water-based, oil-based, or acombination thereof. Liquids may take any known liquid form, such assolutions, slurries, suspensions, dispersions, or emulsions. Liquidforms are preferred since they can be injected or sprayed with precisionvia conventional pumping and metering devices. A preferred means ofadding additives to the coal or fuel oil is via injection in liquidform.

The amount of slag control agent(s) employed can vary depending upon avariety of process and composition conditions, such as type of slagcontrol agent selected, load or feed rate of fuel, amount and type ofoxygen-generating agent used, amount or feed rate of air, impuritycomposition of fuel, and the like. When a liquid form of the slagcontrol agent is used, the amount employed will typically vary fromabout 1:2000 to about 1:6000 agent:agent/fuel oil, volume:volume.

The amount of slag control agent(s) or other additives employed in coalis subject to the same variables as other fuels, and is usuallyexpressed in terms of parts per million (ppm) and weight percent. Theamount of slag control agent(s) employed in terms of “timesstoichiomentry” in reference to a certain emission, such as SO₃. Dosagetypically ranges from about 100 ppm to about 5 weight percent based onthe weight of the coal and may vary depending on the type of additive.

The amount of oxygen-generating agent employed can vary depending upon avariety of process and composition conditions, such as type ofoxygen-generating agent selected, load or feed rate of fuel oil, coal,or biomass, amount and type of slag control agent used, amount or feedrate of air, impurity composition of fuel, and the like. When a liquidform of the oxygen-generating agent is used, the amount employed willtypically vary from about 1:1000 to about 1:10000 and preferably about1:2500 to about 1:4000 agent:coal/fuel oil, volume:volume. Expressed asa function of weight, the amount of slag control agent(s) employedtypically varies from about 25 ppm to about 3 weight percent.

Additives can be employed separately or in combinations of two or moreat the same time and may also be controlled and/or adjusted in real timein accordance with the present invention. The relative ratio of amountor rate of an additive(s) to another additive(s) and/or to the fuel mayalso be controlled and/or adjusted in real time in accordance with thepresent invention.

Fuels useful in the process of the present invention can be of any formknown in the art, such as fuel oil, coal, or biomass.

Coal useful in the process of the present invention can be of any formknown in the art, such as anthracite, bituminous, sub-bituminous,lignite, pet coke, and charcoal.

Fuel oil useful in the process of the present invention is a mixture offlammable, medium-weight hydrocarbons principally used for heating orpower generation. It is alternately referred to as residual oil, #6 oil,Bunker C.

Conventional process components and equipment may be utilized to controland vary the feed rates of the fuel and/or additives. Examples of usefulprocess components and equipment include, but are not limited to, flowlimiting/controlling devices such as valves; pumps; fans; and conveyorbelts.

The process of the present invention is carried out substantiallycontinuously as the operation of a conventional utility boiler issubstantially continuous.

Additional teachings regarding the use of additives in coal-firedutility boilers are found in U.S. Ser. No. 12/319,994, filed Jan. 14,2009, and in oil-fired utility boilers in U.S. Ser. No. 11/311,069,filed Dec. 19, 2005, both of which are incorporated herein by referencein their entireties.

The fuel can be analyzed for a variety of physical and/or chemicalproperties or parameters. Examples of parameters include the following:calorific value (BTUs); volatile matter (VM); ash; moisture; carbon/freecarbon; hydrogen; sulfur; sulfur dioxide; sulfur trioxide; sulfatecompounds; nitrogen; oxygen (by difference); ash fusion temperatures(reducing and oxidizing atmospheres); oxides of silica; alumina; iron;calcium; magnesium; potassium; sodium; zinc; copper; titanium; chlorine;bromine; arsenic; mercury; cobalt; nickel; chromium; lead; and cadmium.

Exhaust gas and flue gas can be analyzed for a variety of emissions.Emissions of interest include SO₂, SO₃, H₂SO₄, NO_(x), NO, NO₂, Hg, andparticulates.

Useful analytical devices and techniques include the following: promptgamma neutron activation analysis (PGNAA), nuclear magnetic resonancespectroscopy (NMR), and laser induced breakdown spectroscopy (LIBS).

In PGNAA, neutrons are emitted from a radioactive source of Cf-252 andare directed at coal and captured by nuclei of elements (coalconstituents). The nuclei become excited and a gamma ray is released(detected by a sodium iodide detector or similar device). The gamma rayenergy is characteristic of each element. Cs-137 may also be used as agamma ray source in some applications.

In NMR, a magnetic field is applied to the sample. The nuclei of thesample absorb the field and radiate the energy back out. The strength ofthe field is radiated back out and identifies the constituents.

In LIBS, a high power laser is used to form a plasma gas from thesample. A spectrometer analyzes the “plume” that is emitted from thelaser pulse to qualify the constituents of the sample.

Other useful analytical devices and techniques include the following:mass spectroscopy (mass spec); inductively coupled plasma spectroscopy(ICP); microwave analyzer for moisture readings; atomic absorptionspectroscopy (AA); optical emission spectroscopy (OES); X-raydiffraction spectroscopy (XRD); X-ray fluorescence spectroscopy (XRF);and pulsed fast and thermal neutron analysis (PFTNA).

In the process of the present invention, the number of physical and/orchemical parameters of the fuel and/or emissions variables subject tomonitoring can be as few as one or plural, i.e., two or more.

It should be understood that the foregoing description is onlyillustrative of the present invention. Various alternatives andmodifications can be devised by those skilled in the art withoutdeparting from the invention. Accordingly, the present invention isintended to embrace all such alternatives, modifications and variancesthat fall within the scope of the appended claims.

1. A process for operating a utility boiler, comprising: a) providingfuel to the boiler; b) providing one or more additives selected from thegroup consisting of (i) one or more slag control agents, (ii) one ormore oxygen-generating agents, (iii) one or more acid reduction agents,(iv) one or more fouling prevention agents, (v) one or more oxidizeragents, (vi) one or more heavy metal capturing agents and (vii) anycombination of the foregoing to the boiler or an auxiliary devicethereof; c) providing air to the boiler; d) burning the fuel in theboiler to generate heat and an exhaust gas and/or a flue gas; and e)intermittently or continuously monitoring one or more physical and/orchemical parameters of the fuel and/or intermittently or continuouslymonitoring one or more emissions variables of the exhaust gas and/or aflue gas to obtain one or more values; and f) varying or maintaining therate at which the one or more additives is provided to the boiler or anauxiliary device based on the one or more values obtained.
 2. Theprocess of claim 1, wherein the one or more values are communicated inreal time to a controller, and wherein the controller providesinstructions based on the one or more values in real time to one or morecomponents of the process to vary the rate at which either or both ofthe fuel and the one or more additives is provided to the boiler and/orits auxiliary devices.
 3. The process of claim 3, wherein the one ormore emissions variables in the exhaust gas are selected from the groupconsisting of opacity, particulates, NO_(x), SO₂, SO₃, acid level, andHg.
 4. The process of claim 1, wherein the one or more additives is oneor more slag control agents selected from the group consisting ofmagnesium hydroxide, magnesium oxide, magnesium carbonate, magnesiumorganometallic compounds, magnesium carboxylate, magnesium salicylate,magnesium napthenate, and magnesium sulfonate.
 5. The process of claim1, wherein the one or more additives is one or more oxygen-generatingagents selected from the group consisting of calcium hydroxide, calciumoxide, calcium carbonate, calcium carboxylate, calcium organometalliccompounds, calcium sulfonate, iron hydroxides, iron oxides, ironcarbonates, iron carboxylates, iron organometallic compounds, ironsulfonates, barium hydroxide, barium oxide, barium carbonate, bariumcarboxylate, barium organometallic compounds, and barium sulfonate. 6.The process of claim 1, wherein the one or more additives is added tothe fuel to form a treated fuel, and wherein the treated fuel is thenprovided to the boiler.
 7. The process of claim 1, wherein the one ormore additives is provided directly to the boiler.
 8. The process ofclaim 1, wherein the fuel is coal
 9. The process of claim 1, wherein thefuel is fuel oil.
 10. The process of claim 1, wherein the fuel isbiomass.
 11. The process of claim 2, wherein the one or more componentsis selected from the group consisting of a flow limiting/controllingdevice, a pump, a fan, or a belt speeds.
 12. The process of claim 1,wherein the physical and/or chemical parameters of the fuel aremonitored by a technique selected from the group consisting of one ormore of prompt gamma neutron activation analysis, nuclear magneticresonance spectroscopy, laser induced breakdown spectroscopy, massspectroscopy; inductively couple plasma; microwave analyzer for moisturereadings; atomic absorption; optical emission spectroscopy; X-raydiffraction; X-ray fluorescence; and pulsed fast and thermal neutronanalysis.
 13. The process of claim 1, wherein the physical and/orchemical parameters of the fuel is selected from the group consisting ofone or more of calorific value; volatile matter; ash; moisture;carbon/free carbon; hydrogen; sulfur; sulfur dioxide; sulfur trioxide;sulfate compounds; nitrogen; oxygen (by difference); reducing andoxidizer ash fusion temperatures; and one or more oxides of any ofsilica, alumina, iron, calcium, magnesium, potassium, sodium, zinc,copper, titanium, chlorine, bromine, arsenic, mercury, cobalt, nickel,chromium, lead, and cadmium.
 14. The process of claim 1, wherein furtherin step (e) the exhaust gas and/or a flue gas is intermittently orcontinuously monitored with respect to one or more emissions variablesto obtain one or more additional values, wherein varying or maintainingthe rate at which either or both of the fuel and the one or moreadditives is provided to the boiler based on the one or more additionalvalues obtained, and wherein the one or more emissions variables ismaintained within pre-determined limits.
 15. The process of claim 1,wherein in step (e) the one or more physical and/or chemical parametersof the fuel is intermittently monitored.
 16. The process of claim 16,wherein in step (e) the one or more physical and/or chemical parametersof the fuel is intermittently monitored at a period of time elapse offive minutes or less between the end of a test and repeat of the test.17. The process of claim 1, wherein the physical and/or chemicalparameters of the fuel is selected from the group consisting of ash;sulfur; and one or more oxides of any of silica, alumina, iron, calcium,magnesium, potassium, sodium, copper, titanium, chlorine, bromine,arsenic, and mercury.
 18. The process of claim 1, wherein the one ormore additives are provided to the boiler.
 19. The process of claim 1,wherein the rate at which the one or more additives is provided to theboiler is varied or maintained based on the one or more values obtained.